Use of tannic or gallic acid to produce low beverage soluble iron content filter aid

ABSTRACT

A low beverage soluble iron content filter aid, especially diatomite, is disclosed, as is the method for its production, which comprises contacting the granular filter aid with tannic acid, gallic acid, or mixtures thereof, preferable in aqueous solution. Color control agents such as citric acid may also be present in the solution. The treated filter diatomite is useful in the filtration of vegetable based beverages, especially beer, wine, ale and fruit juices. The invention is also applicable to other filter aids which contain beverage soluble iron, such as perlite.

BACKGROUND OF THE INVENTION

The invention herein relates to filter aids, especially diatomite,having a low soluble iron content. It also relates to a method forproduction of such low soluble iron filter aid.

In the manufacture or processing of a number of vegetable basedbeverages (notably beer, ale, wine and fruit juices) the beverage isfiltered one or more times through granular heterogeneous filter media,usually diatomite. These filter media contain small amounts of variousminerals and compounds, among which are iron compounds. A certain smallportion of the iron content of the media is soluble in the vegetablebeverages. This portion of the iron may be referred to as "beveragesoluble iron" (often abbreviated "BSI").

The presence of higher levels of BSI dissolved in the beverage can bedeleterious to the taste and long term stability ("shelf life") of thebeverage. Consequently, it would be desirable to have a filter mediumwhich is low in BSI content but which retains its desirable filtrationand clarification properties.

BRIEF SUMMARY OF THE INVENTION

The invention herein is a method for the production of low beveragesoluble iron content filter aid, especially diatomite, which comprisescontacting granular filter aid containing a initial content of beveragesoluble iron with an aqueous solution of tannic acid, gallic acid ormixtures thereof to reduce that beverage soluble iron content. Colorcontrol agents such as citric acid may also be present in the solution.Also a part of the present invention is a filter aid low in beveragesoluble iron content produced in accordance with this method.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

The basic material used in the process of the invention is a granularfilter aid which initially contains beverage soluble iron. ("Initially"herein refers to the BSI content immediately prior to the treatingprocess of this invention. The filter aid by that time will probablyhave already undergone prior processing which may have altered the BSIcontent of the original material such as crude ore from which the filteraid is made.) For convenience the invention herein will be discussed interms of diatomite, since this is the common and preferred filter aidfor vegetable beverages. However, it will be understood that the processis also applicable to other filter aids, such as perlite and clays,which contain beverage soluble iron. The considerations discussed belowfor diatomite will be similarly applicable to these other filter aids.

Diatomite is a naturally occuring material found in deposits in variousparts of the world. It is formed by the deposition over many years ofthe siliceous skeletons of ancient microscopic marine organisms known asdiatoms. Commercial deposits are found in California, Oregon, Washingtonand several other states, as well as in several foreign countries. Thechemical composition of a typical diatomite is 85 to 90% silica, 2 to 4%alumina, 1 to 2% ferric oxide, and small amounts (less than 1%) ofmaterials such as magnesia, lime, alkalies and titania. There are alsotypically up to about 5% volatile materials including water, carbondioxide and organics.

After being mined the diatomite (which is also frequently known as"diatomaceous earth") may be crushed, screened, calcined and classifiedto separate it into a variety of grades of different granular sizes,purities and reactivities. The grade of diatomite and the variousconventional steps of handling and processing are not particularlycritical to the present invention. The presence of beverage soluble ironis in part a function of the chemical composition of the original ore.The type of conventional (largely mechanical and thermal) processingtechniques used to produce the commercial grades of diatomite may effectthe overall amount of BSI in the final diatomite product. However, thisinvention is generally applicable to all varieties of diatomitecontaining significant quantities of beverage soluble iron.

In the process of the present invention the beverage soluble ironcontent of the diatomite is reduced by contacting the granulateddiatomite with an aqueous solution of tannic acid, gallic acid ormixtures of these acids. Tannic acid (also known as gallotannic acid andtannin), is a naturally occuring substance found widely in plants,particularly oak and sumac. The exact molecular formula is unknown butis believed to be a mixture of a number of gallic acid derivatives. Atypical published formula is C₇₆ H₅₂ O₄₆ with a molecular structure of##STR1## wherein R is galloyl, m-digalloyl, or m-trigalloylsubstituents. Typical commercial physical properties of tannic acid arethat it decomposes at about 210° C.; may be in the form of powder,flakes or a spongy mass; is odorless; has a strong astringent taste; andis soluble in water, alcohol and acetone and almost insoluble inbenzene, chloroform and ether.

Gallic acid (3,4,5-trihydroxybenzoic acid) is commonly in the form ofcolorless or slightly yellow crystalline needles or prisms which aresoluble in alcohol and glycerol and sparingly soluble in water andether. It has a specific gravity of 1.7 and a melting point ofapproximately 230° C. It is commonly produced by the action of mold onsolutions of tannin or by boiling tannin with strong acid or causticsoda.

In the present invention the diatomite is treated by contacting withaqueous solutions of tannic acid, gallic acid or mixtures of these two.The solution will normally contain 1% to 20% acid by weight although thestrength of the acid solution is not critical. The amount of acid(measured as acid rather than solution) useful in the present processwill be in the range of from 0.1 to 1.5 gm-moles of acid per ton ofdiatomite, preferable 0.2 to 1.2 gm-moles of acid per ton of diatomite.

Contacting may be accomplished by any of several means. The acidsolution may be sprayed on the diatomite while the latter is beingclassified by suspension in an air stream. Alternatively the diatomitemay be simply washed with the acid, as for instance being put through abath of the acid solution, or having the acid poured through a layer ofthe diatomite. Other conventional liquid/solid contacting means such asfluidized beds may also be used. The particular choice of technique tocontact the acid and diatomite will often be based on availableequipment, economics and similar criteria.

The time of contact will vary according to the strength of the acidsolution and the amount of beverage soluble iron present in thediatomite (a typical analysis of diatomite shows 45 to 55 ppm of BSI).The contact time may be very short, such as merely the time it takes toform a slurry of the diatomite in the solution and filter it. Theoptimum treating time for any specific sample of diatomite and strengthof acid can be readily determined by routine experimentation.

If desired the diatomite and/or acid solution may also be heated to atemperature on the order of 90° C. to 100° C. prior to contacting toexpedite the reaction by which the acid reduces BSI from the diatomite.The exact nature of this reaction is not known, but it is believed thatthe BSI is reduced by being complexed with the acid.

Following the acid contacting the diatomite may be washed with water toremove the acid and any extracted iron. If desired a plurality of rinsesmay be used, the rinse water may be heated, and/or varying lengths ofrinse period may be used. However, rinsing is not mandatory, for afterbeing treated with the acid the iron solubility in the beverages isreduced whether it remains on the diatomite or is removed by rinsing.The optimum rinse techniques, if any, will be a simple matter of choicefor one skilled in the art.

If desired, the aqueous solution of tannic and/or gallic acid may alsocontain color control agents. These acids have a tendency to impart darkcolor to solutions, and the color control agents react with any excessacid to reduce that tendency, thus discolorizing the solutions. Suitablecolor control agents include citric acid, sodium sulfite, potassiumbromate, and ethylene diamine tetraacetric acid. Levels of concentrationof these agents will be a matter of routine choice, but typical levelswhich have been found satisfactory are 0.2 to 0.3 molar in a solutionwhich is 0.04 molar in tannic and/or gallic acid.

The following examples will illustrate the process of this invention. 50gm samples of a flux calcined California diatomite containingapproximately 45 to 55 ppm BSI was pre-heated to approximately 200° F.(93° C.) for three hours. Aqueous solutions of acid were made up using17% acid in water. Each sample of heated diatomite was put into ablender which was equiped with heating means for maintaining the preheattemperature. Agitation of the diatomite to form an air suspension wasobtained by the blender blades. The acid was sprayed into the blenderjar. Complete dispersion of the acid through the diatomite was obtainedin approximately 2 minutes. The diatomite was then dried and the BSIconcentration determined.

In an alternative technique a filter cake was formed on a Buchner filterusing 50 gm of diatomite and water. The filter cake was then washed with500 ml of 17% acid solution. The acid remained in contact with thefilter cake for approximately 10 minutes. Thereafter the filter cake wasrinsed with water, dried, and BSI concentration determined. Results werefound to be equivalent to the spray technique.

Typical results are presented in the table below.

    ______________________________________                                                 Dosage          Reduction                                                     lb acid/ton diatomite                                                                         of BSI, %                                            ______________________________________                                        Tannic Acid                                                                              0.9               30                                                          1.7               50                                                          1.8               35                                                          1.9               53                                                          3.3               70                                                          3.6               68                                               Gallic Acid                                                                              0.43               7                                                          0.85              35                                                          0.95              12                                                          1.9               30                                                          2.9               40                                               ______________________________________                                    

It will be evident from these data that the process of the presentinvention significantly reduces the amount of beverage soluble ironpresent in diatomite filtrates. The resultant low beverage soluble ironcontent diatomite therefore makes a superior filtration medium forvegetable beverages for it substantially reduces the amount of ironwhich is extracted by the beverage from the diatomite during filtration.

Other contacting fluids were experimented with to determine if therewere other materials equivalent to tannic and gallic acids. Water,starch, sucrose, monobasic sodium phosphate, tartaric acid, gluconicacid, salicylic acid, and the sodium salt of ethylene diaminetetraacetic acid were all tried. The organic acids in this groupproduced only insignificant reduction in BSI. The remaining materialswere able to reduce BSI by larger amounts than the organic acids, buttook long time periods (often 10 days to 2 weeks) to reach the BSIreduction levels obtained with tannic and gallic acids in a matter ofminutes.

What is claimed is:
 1. A method for the reduction of the beveragesoluble iron content of a filter aid comprising diatomite or perlitewhich comprises contacting the filter aid in granular form with tannicacid, gallic acid or mixtures thereof.
 2. A method as in claim 1 whereinsaid filter aid comprises diatomite.
 3. A method as in claim 2 whereinsaid tannic acid, gallic acid or mixture thereof is in aqueous solution.4. A method as in claim 3 wherein said aqueous solution has aconcentration of 1% to 20% acid by weight.
 5. A method as in claim 3wherein solution also contains a color control agent.
 6. A method as inclaim 5 wherein said color control agent is citric acid, sodium sulfite,potassium bromate or ethylene diamine tetraacetic acid.
 7. A method asin claim 2 wherein said contacting comprises spraying the diatomite withthe acid.
 8. A method as in claim 2 wherein said contacting compriseswashing the diatomite with the acid.
 9. A method as in claim 2 whereinthe acid is contacted in an amount of 0.1 to 1.5 gm-moles of acid perton of diatomite.
 10. A method as in claim 9 wherein the acid iscontacted in an amount of 0.2 to 1.2 gm-moles of acid per ton ofdiatomite.
 11. A method as in claim 2 wherein said acid comprises tannicacid.
 12. A method as in claim 2 wherein said acid comprises gallicacid.
 13. A method as in claim 2 wherein said acid comprises a mixtureof tannic acid and gallic acid.
 14. A filter aid comprising diatomite orperlite which has had its initial content of beverage soluble ironreduced by treating the diatomite in accordance with the method ofclaim
 1. 15. A filter aid comprising granulated diatomite which has hadits initial content of beverage soluble iron reduced by treating thediatomite in accordance with the method of claim
 2. 16. A filter aidcomprising granulated diatomite which has had its initial content ofbeverage soluble iron reduced by treating the diatomite in accordancewith the method of claim
 9. 17. A filter aid comprising granulateddiatomite which has had its initial content of beverage soluble ironreduced by treating the diatomite in accordance with the method of claim11.
 18. A filter aid comprising granulated diatomite which has had itsprior content of beverage soluble iron reduced by treating the diatomitein accordance with the method of claim 5.